The four side boosters (Blocks B, V, G and D) form the first stage of the Soyuz launcher and are arrayed around the central core. This architecture is derived from the R-7 Semyorka missile developed by the Soviet Union in the early 1950s. Standing 20 metres tall, each booster is powered by an RD-107A engine with four large combustion chambers fuelled with liquid oxygen and kerosene, and has two vernier thrusters for steering. After lift-off, the four boosters burn for 118 seconds and are then jettisoned.
Standing 28 metres tall and spanning 2.95 metres, the second stage (Block A) is the central core of the launcher. It is powered by an RD-108A main propulsion engine comprising four chambers and four vernier thrusters for steering. Like for the side boosters, the RD-108A is fuelled with liquid oxygen and kerosene. Second stage ignition occurs at the same time as the first stage and generates 400 tonnes (4146 kN) of thrust. The stage burns for 286 seconds.
The third stage (Block I) sits atop the second stage and is 6.7 metres tall. Like the first and second stages, it is fuelled with liquid oxygen and kerosene (all three Soyuz stages use the same propellants). It is powered by an RD-0110 engine for the Soyuz ST-A variant or a more powerful RD-0124 for the Soyuz ST-B. Third stage ignition occurs two seconds before shutdown of the second stage and it burns for 230 seconds. Separation from the central core is commanded by the flight computer.
FREGAT UPPER STAGE
The Fregat upper stage is fully autonomous and designed to operate as a separate spacecraft. Light, very precise, powerful and able to restart several times in flight, it was developed specifically for Soyuz-2 by Russian firm NPO Lavochkin from the propulsion modules built for the Phobos and Mars96 probes. Flight qualified in 2000, it stands 1.5 metres tall, spans 3.3 metres and has an empty weight of approximately 1,000 kilograms. The upper stage consists of six spherical tanks—four for propellants, two for avionics—arrayed in a circle around the main S5-92 engine providing two tonnes of thrust, with trusses passing through the tanks to provide structural support. The four tanks are filled with unsymmetrical dimethylhydrazine (UDMH) and nitrogen tetroxide (NTO or N2O4) propellants, with two tanks for each. The two avionics fuel tanks comprise electronic equipment racks for flight computers and command, telemetry and navigation units.
Fregat is independent from the lower three stages; indeed, the Russians make a clear distinction between the Soyuz launcher—the first three stages—and the Fregat upper stage, which has its own guidance, navigation, control, tracking and telemetry systems. The stage can restart up to 20 times in flight, thus enabling it to place payloads very precisely into their final orbit. It has the capability to operate autonomously for 48 hours after lift-off.
Soyuz-ST can loft up to:
- 4.8 tonnes to low Earth orbit (LEO)
- 3.2 tonnes to geostationary transfer orbit (GTO)
The payload may consist of a single satellite or several satellites.
Soyuz ST’s fairing spans 4.1 metres and stands 11.4 metres tall. It is larger than the Soyuz-1 fairing (3.7 metres across and 7.7 metres tall).